I've heard it explained that "hey" used to be more of an urgent way to get someone's attention, rather than a casual "hello" like it is now, so it sounded rude to some older folks.
My daughter is not allowed to call me 'dude' or 'bro.' I don't care if that's old fashioned or closed minded of me. I like being called Dad or Daddy, and shouldn't it be my choice what I'm called?
really its cultural and traditions vs modernity and respect vs loving, etc. maybe her showing what you feel is disrespect is her showing informal comfort. maybe if you want her to keep calling you at all in a few years you can love her as you find her. the world is harsh enough to teach her plenty without you being a bridge troll to her safe space.